Bill isn't showing up yet — if it's been fewer than 24-48 hours since the expected issue date, PITC probably hasn't received it from the DISCO yet; try again the next day rather than assuming something's broken.
Amount looks too high — the first check is always the previous month's unit count, not the rupee total. A sudden jump usually traces to a faulty meter, an estimated (not actual) reading, or an appliance that got left running; a call to your DISCO subdivision office gets a meter check scheduled.
Reference number won't work — it has to be exactly 10 to 14 digits, no letters, no spaces. Older meters occasionally get reassigned a new reference number during system upgrades, in which case your local DISCO office can confirm the current one.
Due date already passed — a Late Payment Surcharge applies from that point on and keeps accruing, so pay as soon as you can rather than waiting; letting it run risks disconnection.
Arrears showing on the bill — these are unpaid balances carried forward from earlier cycles rather than a new charge. Clearing them stops them compounding and avoids disconnection action later.